1. Field of the Invention
The present invention relates to pressure transducers and, more particularly, the present invention is directed to a disposable transducer apparatus for use in an electromanometry system for monitoring and recording hemodynamic pressures.
2. The Prior Art
With the advent of high speed digital computers in the 1950's and 1960's, a number of medical teams throughout the United States began considering the possibility of computerized blood pressure monitoring. Today, computerized blood pressure monitoring systems are frequently used in intensive care facilities to provide around-the-clock computer monitoring of hemodynamic pressures in critically ill heart patients both during and following cardiovascular surgery and the like.
As the heart pumps, the resistance to fluid flow and elasticity of the blood vessels cause a buildup in the arteries of a continuous mean blood pressure having a superimposed fluctuation between a maximum and minimum pressure, known as systolic and diastolic pressures, respectively. It is the function of a computerized blood pressure monitoring system to continuously measure and electronically record measurements of the cyclical blood pressures which occur by virtue of the heart's pumping action.
In order to transform these measurements of cyclical blood pressures into recordable electronic waveforms, a catheter filled with a sterile saline solution is inserted into a patient's artery and is threaded through the artery until the tip of the catheter is located near the heart. In this way, the periodic pulsations of blood are transmitted as mechanical pulses of fluid through the saline-filled catheter. The catheter tubing is connected to a pressure transducer which converts the mechanical pressure pulses through the saline in the catheter into electronic waveforms that may be visually displayed on an oscilloscope screen or on a recording strip chart. These electronic waveforms are subsequently analyzed by a computer to determine a number of quantitative parameters, including heart rate, duration of systole, and systolic, diastolic and means pressures. This information gives the surgeon and other health care personnel a quantitative look at the operation of a patient's heart, and is thus extremely valuable in helping to assess the clinical course of critically ill patients on a continuously updated basis.
The pressure transducers typically used in an electromanometry system are relatively expensive. Thus, in the past the practice has been to resterilize the transducer after using it on a patient so that it could be used anew on other patients. This practice tended to increase the risk of cross-contamination among patients, and also resulted in increased maintenance costs and inconvenience. Moreover, because such transducers are expensive, if one was accidentally damaged or dropped, the expense to the hospital became significant. A further disadvantage of the prior art transducers is their size and weight. Because of these size and weight considerations prior art pressure transducers were mounted on brackets attached to a standard I.V. pole. This separate mounting caused inconvenience and undue complication when setting up the electromanometry system or transporting the patient. The prior art type transducers also require frequent calibration, thus adding to the maintenance costs and inconvenience already present with these devices.
In an effort to reduce the expanse and inconvenience associated with having to resterilize non-disposable transducers after each use, disposable pressure transducer domes have been developed which physically isolate the transducer from the saline solution carried by the catheter tubing. The disposable transducer domes typically consist of a thin plastic membrane which is used to physically separate the diaphragm of the transducer from the saline solution so that the diaphragm is not contaminated by the saline solution, which has been in contact with the patient's blood. Although such disposable transducer domes help to minimize the risk of contamination and also help to reduce the cost associated with resterilization of pressure transducers, the plastic membrane attenuates the mechanical pressures transmitted through the saline solution, with the result that the resulting electronic waveforms are often degraded in quality.
Further efforts to improve the state of the art concerning pressure transducers used in connection with blood pressure monitoring have included efforts to develop smaller, miniaturized versions of the pressure transducer. The smaller, miniaturized pressure transducers, although much reduced in size so that they can be directly supported on the arm of the patient or by the pressure tubing, nevertheless are expensive to construct and are still intended to be reused, thus requiring continued use of disposable transducer domes.
Thus, what is needed in the art is a very small, light-weight transducer which is sufficiently economical in its construction as to be disposable after each use, thus eliminating the need for resterilization techniques and also eliminating the need for using disposable transducer domes.